IRS Definition of Lobbying Expenditure Test

Basic Requirements
The communication must address ?specific legislation, which includes bills, resolutions, repeal proposals, referendums or similar items at the federal, state and local level. It also includes specific proposals that have not yet been introduced in a legislative body.
Source: IRS Reg. IRS Regulations Sec. 56.4911-1 and Reg. 56.4911-2(d)(1)(ii).

Direct Lobbying v. Grass Roots Lobbying

Membership Communications
Communications made primarily to members as internal to the organization, and therefore communications that express a view on specific legislation but contain no direct ?call to action? do not constitute direct or grassroots lobbying. A member is defined as someone who contributes more than a nominal amount of time or money to the organization. A communication that asks members to contact legislators constitutes direct lobbying, but if it urges members to ask the general public to contact legislators it constitutes grassroots lobbying. If there is a call to action and the audience is primarily but not 100% members, the cost is divided between direct and grassroots lobbying.
Source: IRS Reg. 56.4911-5

Call to Action
State that the recipient should contact a legislator or other relevant government employee for the purposes of influencing legislation; OR state the address, telephone number or similar information regarding a legislator or legislative body employee; OR provide a petition, post card of similar means for the recipient to contact a legislator or legislative body employee; OR specifically identify a legislator or legislators who will note on the legislation as being opposed to undecided about the organization's view on the legislation; OR a member of a legislative (sub)committee which will vote on the legislation. But note that identifying the sponsor of a bill is NOT a call to action.
Source: IRS Reg. 56.4911-2(b)(2)(iii)

Paid Mass Media Advertisements

• General educational messages that do not contain a "call to action" but do reflect a view on the same specific subject as highly publicized legislation are presumed to be grassroots lobbying communications (and therefore expenses) ONLY when they appear within two weeks of a vote by a legislative body (including committees and subcommittees). "Highly publicized" means the legislation receives frequent media coverage within two weeks of its voting AND the general purposes, terms, and pending action of the legislative body must be known to a significant portion of the public in the area where the ad appears.

• The presumption can be rebutted if the organization can show that the timing of ad was unrelated to the upcoming legislative vote (i.e. the ad was simply part of a regular or ongoing series of communications around an issue).

• The rule also applies to ads that encourage the public to contact legislators about the general subject of legislation (but not specific legislation) and appear within two weeks of a vote.